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M23-20

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Math Expert
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M23-20  [#permalink]

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New post 16 Sep 2014, 01:19
1
3
00:00
A
B
C
D
E

Difficulty:

  25% (medium)

Question Stats:

82% (01:57) correct 18% (02:23) wrong based on 191 sessions

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Math Expert
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Re M23-20  [#permalink]

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New post 16 Sep 2014, 01:19
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Joined: 17 May 2016
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GMAT 1: 740 Q46 V46
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Re: M23-20  [#permalink]

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New post 19 Dec 2016, 10:08
Hi,

Is it possible to calculate it algebraically ?

I get stuck with two unknown, even if I know that is quicker to back solve, I do not understand why it is not solvable ?

Many thanks in advance for your kind help
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Re: M23-20  [#permalink]

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New post 19 Dec 2016, 10:18
nickimonckom wrote:
Hi,

Is it possible to calculate it algebraically ?

I get stuck with two unknown, even if I know that is quicker to back solve, I do not understand why it is not solvable ?

Many thanks in advance for your kind help


Which two unknowns are you talking about? There is only one unknown in the equation above. If you simplify \(\frac{60}{x} = \frac{60}{x + 20} + 0.5\) you'll get quadratic equation which will give two values of x: -60 (discard) and 40.
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Re: M23-20  [#permalink]

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New post 20 Dec 2016, 02:53
I mean that if I set up the table, I get the following :

FIRST MOVE : \(r*(t+\frac{1}{2}) = 60\)
2ND MOVE : \((r+20)*t = 60\)

Then, since they are equal :
\(r*(t+\frac{1}{2}) = (r+20)*t\)
\(rt + \frac{r}{2} = rt + 20t\)
\(r = 40t\)

Then I have a problem with the unit, I know that 40 is the good value but I am not supposed to express a rate and a time, only a rate.

thanks in advance for your help
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Re: M23-20  [#permalink]

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New post 06 Apr 2017, 22:33
Could you please share some links to questions similar to this? Thank you.
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Re: M23-20  [#permalink]

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New post 07 Apr 2017, 00:29
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Concentration: Marketing, General Management
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Re: M23-20  [#permalink]

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New post 09 Apr 2018, 12:05
For those of you wanting to set up an equation and solve it w/o plugging in, I can chime in to help.
Since traveling at 20kmh faster saves 1/2 hour, we can say that:
60/R - 60/(R+20) = 1/2, which is basically saying:
(Time at Reg Speed) - (Time +20kmh faster) = (30 mins)

Solving, we get:
(R+60)(R-40)=0
R= -60, 40

Rate can not be negative, therefore, 40 is the winner.
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Re: M23-20  [#permalink]

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New post 14 Jan 2019, 12:23
I used the options.

60/40= 1.5 60/60=1

B is the only one that fits.
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Re: M23-20   [#permalink] 14 Jan 2019, 12:23
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